1. The Field of the Invention
This invention relates in general to fiber optics, and in particular to devices and methods of coupling optical fibers to light sources of light responsive circuits or other optical fibers.
2. Description of Related Art
Optical fibers are flexible transparent fiber devices used for either image or information transmission in which light is propagated by total internal reflection. In simplest form, the optical fiber or light guide consists of a core of material with a refractive index higher than the surrounding cladding.
There are three basic types of optical fibers. In a multimode, stepped-refractive-index-profile fiber, the number of rays of light which are guided, and thus the amount of light coupled into the light guide is determined by the core size and the core-cladding refractive index difference. Such fibers, used for conventional image transfer, are limited to short distances for information transmission due to pulse broadening. An initially sharp pulse made up of many modes broadens as it travels long distances in the fiber, since the high-angle modes have a longer distance to travel relative to the long-angle modes. This limits the bit rate and distance because it determines how closely input pulses can be spaced without overlap at the output end.
The graded index multimode fiber, where the core refractive index varies across the core diameter, is used to minimize pulse broadening due to intermodal dispersion. Since light travels more slowly in the high index region of the fiber relative to the low index region, significant equalization of the transit time for the various modes can be achieved to reduce pulse broadening. This type of fiber is suitable for intermediate-distance, intermediate-bit-rate transmissions systems. For both fiber types, light from a laser or light emitting diode can be effectively coupled into the fiber.
A single-mode fiber is designed with a core diameter refractive index distribution such that only one mode is guided, thus eliminating intermodal pulse-broadening effects. Interior waveguide dispersion effects cause some pulse broadening, which increases with the spectral width of the light source. These fibers are best suited for use with a laser source in order to effectively couple light into the small core of the light guide, and to enable information transmission over long distances at very high bit rates. The specific fiber design and ability to manufacture it with controlled refractive index and dimensions determines the ultimate bandwidth or information carrying capacity.
The problem of joining fibers together or joining fibers to light emitters or light receivers, has been approached in two ways. For permanent connections, the fibers can be spliced together by carefully aligning the individual fibers and then epoxying them together or fusing them together. In fact, permanent connection of fiber ribbons (linear array of several fibers) can be achieved by splicing the entire ribbon as a single unit. For temporary connections, or for applications in which it is not desirable to make splices, fiber connectors have been developed. In order to provide further background information so that the invention may be completely understood and appreciated in its proper context, reference is made to the following prior art patents and publications.
U.S. Pat. No. 3,779,628 to Karpon et al discloses an optical waveguide light source coupler for coupling a large coherent light source to an optical fiber. A feature of this design is the frusto-conic core of the coupler. The front of the coupler is flat, allowing a flat emitter such as a diode laser, to be attached directly to the coupler. The cladding of the optical fiber serves only to internally refract light into the core. This coupler has only two distinct layers of material with different refractive indices, and is interposed between the end of the fiber and the light source.
U.S. Patent No. 4,844,580 to Lynch et al discloses a combination lens and sleeve made from a glass capillary tube. The end of the tube is melted with a flame as it is rotated to form the lens that focuses the light on the end of the fiber. The conical cavity between the end of the fiber and the bulbous end must be filled with an index matching fluid or glue to make the design effective. Light is only propagated into the fiber at the end of the fiber. The bulbous lens sleeve is manufactured separately and must be fitted over the end of the fiber, thus requiring a number of processing steps.
Fiber Optics, Advances in Research and Development, ed. B. Benden et al, pp. 437-473, (Plenum Press 1978) surveys a B. Benden et al, number of related designs of devices for centering optical fibers within connector bodies. As identified in the above-cited book, fiber connectors suffer from ray transfer loss due to the misalignment of the coupled optical fibers. Three types of misalignment can exist: end separation, axial displacement, and axial angular tilt. The misalignment losses aggregate and contribute to coupling inefficiency. Furthermore, Fresnel reflections add to the cumulative effect of the coupling losses. These losses can be quite substantial and highlight the need for accurate coupling of the optical fibers. A subsection entitled "Precision Transfer Molded Single Fiber Optic Connector" discusses a method of forming precision molded thermoplastic plugs directly on the optical fiber. The only properties of interest are mechanical, e.g., shrinkage, abrasion resistance, ease of production, and precision. Since this design optimizes optical fiber alignment, any optical transmissions within the plug constitute undesirable cross-talk.
The prior art does not disclose a large scale fiber optic wiring harness and particularly a harness for coupling a relatively large light source wherein the light source energy may be incoherent and polychromatic. A large scale fiber optic wiring harness typically consists of a one-dimensional row of coupled optical fibers or a matrix of optical fibers. Applications of these types of harnesses include image transfer and data transfer. There are two basic types of image transfer techniques. The first technique involves scanning a row of fiber optics in a harness over an image so that the row harness transfers discrete lines of image data. The second type of harness is the matrix harness in which a plurality of fibers are aligned in rows and columns and the entire image is or substantial portions thereof are transferred simultaneously on a pixel by pixel basis. Due to the large number of fiber connectors involved, the process of coupling the fibers to the retaining bracket must be automated to be economically viable.
One object of the present invention is to efficiently condense the light energy into an optical fiber and be manufactured continuously on a large scale to realize a lower cost than other designs. Of the above cited references, none of them achieves or fulfills the purposes of the precision focusing and locating collar of the present invention.
Accordingly, it is another object of the present invention to achieve the efficient collection of incoherent polychromatic light energy from a diffuse source into a fiber optic waveguide.
It is yet another object of the present invention to allow the collecting end of the fiber optic waveguide to be easily and precisely located in a retaining body.